A synchronization unit of this type is known from DE 32 08 945 A1. The known synchronization unit is provided for a positive dual clutch of a gearwheel mechanism which is used, in particular, in the automotive field. The known synchronization unit has a working shaft which is designed as a gear mechanism shaft and on which the sleeve carrier is arranged in a rotationally and axially fixed manner. The sleeve carrier is surrounded in a rotationally fixed manner by a selector sleeve which can be moved axially relative to the sleeve carrier. In each case one clutch gear, which is fastened to a corresponding gearwheel of the gearwheel mechanism, is provided on opposite axial sides of the sleeve carrier. The sleeve carrier is assigned two axially movably mounted synchronizer rings of two synchronizer clutches which are arranged so as to lie opposite one another, which synchronizer rings can be displaced axially by pressure pieces which are mounted on the sleeve carrier. A multiple disk assembly is arranged between each synchronizer ring and the adjacent clutch gear, which multiple disk assembly is pressed together by corresponding axial pressure loading of the respective synchronizer ring and can thus transmit a torque, frictionally, to the clutch gear. The movement of the pressure piece is carried out by axial displacement of the selector sleeve which can be moved via a manual linkage or the like. After rotational speed equalization has been carried out between the synchronizer ring and the associated clutch gear, the selector sleeve is displaced to such an extent that a positive rotational drive can be achieved between the synchronizer ring and the clutch gear. For this purpose, the selector sleeve is provided with an inside axial toothing system. On the same pitch circle diameter, the clutch gear and the associated synchronizer ring have complementary external toothing systems which are likewise configured as axial toothing systems. The construction and function of the synchronizer clutch for the other axial side of the sleeve carrier corresponds in construction and function to that described above.